The present invention relates to a computing system which comprises a plurality of computers, each of which independently executes operational processing, an external storage device which stores shared data accessed by the plurality of computers, and a relay device which receives a request for an access to data stored in the external storage device from each of the plurality of computers to relay the access request to the external storage device.
With an increase in the amount of data used in computers, techniques have been utilized for connecting a plurality of storage devices external to the computers through a network. According to the techniques, data stored in the storage devices connected to the network can be shared by a plurality of computers connected to the network. When a plurality of computers share data stored in a storage device, the consistency of data must be ensured by an exclusive access control or other techniques for limiting accesses to data from remaining computers while the data is being accessed by a certain computer. One of techniques which implements the exclusive access control employs Reverse/Release commands in the SCSI protocol described in “Draft Proposed American National Standard for Information System SCSI-3 Primary Commands,” 28 Mar., 1997, pp. 70-72 and pp. 88-93 (hereinafter called the “prior art document”). This technique enables the exclusive access control in logical block addresses.